Electronic musical instruments with tone generating,mixing,and distributing systems



June 2, 1970 MASUO OMURA ETAL 3,515,039

ELECTRONIC MUSICAL INSTRUMENTS WITH TONE GENERATING, MIXING, AND DISTRIBUTING SYSTEMS Original Filed Jan. 25, 1965 6 Sheets-Sheet 1 l0 FUND 0% FIG I sua 100% FUND 45% SUB 5596 N FUND 60% sue 40% FU/V07596 D/V f sue 2596 FUND 90% \jf sua /0% (x FUND /00% sue 094 FIG. 4

INVENTORS mm WHO muvoo ATTORNEYS June 1970 MASUO OMURA ETAL 3,51

ELECTRONIC MUSICAL INSTRUMENTS WITH TONE GENERATING, MIXING, AND DISTRIBUTING SYSTEMS Original Filed Jan. 25, 1965 6 Sheets-Sheet 2 FIG. 2

F RE QUE NC Y L L A A N 8 L 2 L 3 4 5 6 0 L 0 L 6 m w M w M Q m 6 m 6E P N w w M s m 5 m M L 5 L w. m v N a m L A 8 mm M m M 10... ll: E a ,w w 5 E 0 a a A L m U 5 V N N W L M w I lmLw limb IIMW s 6 6 0 /7 5 A r B 4 6 D N w m w W E n m\ 0 m M C 5 0 6 B 5 0 N U 2 6 U llfi |w f w 5 m M 9 m w 1 L lm NQRQQRQY WQNQQQQQY WQNQQQQY .wQbkfiFkiv MQNQNQSG .WQ\R\QD$$ S Gm EQKQQQM kmtqmmw kwh mm mtqmwh INVENTORS ATTORNEYS June 2, 1970 MASUO OMURA ETAL ,5

ELECTRONIC MUSICAL INSTRUMENTS WITH TONE GENERATING,

MIXING, AND DISTRIBUTING SYSTEMS Original Filed Jan. 25, 1965 6 Sheets-Sheet 5 w x m d. 0 0 0 0 00 0 0.. 0 00 00 m m 7 6 4 2 m /0 m0 0 0 D D 0 0 0 0 0 0 0 N N N mm MM MM MM MM WM MM MM MM WM WM f 1 1 u n n 0 u a u n n u g M 4% v5 3 T m g @afnfl Faro? Qswfiaa Farm. cfiafiawazrswofi Quin? EFEMDUQLMAMQ Faro c on .R HSE NSF. 5T 8 9 0 7 8 9 w mmwwm 5 5 m w A MN 4 8 9 0 W MGQ 3 Qhaafl 3 Qafihaa 4 imrfia 4 w W W W W 0 Q 0 D 0 D N 3& zrs oofi 4 wrzw f WFEfioNS 4 firs oof N W W 0 0 D 0 ATTORNEYS June 1970 MASUIO OMURA ETAL 3,

ELECTRONIC MUSICAL INSTRUMENTS WITH TONE GENERATING,

' MIXING, AND DISTRIBUTING SYSTEMS Original Filed Jan. 25, 1965 6 Sheets-Sheet 4 INVENTOR S H969 HIKO TbbLA/UO ATTORNEYS June 2, 1970 MASUO OMURA ETAL 3,5 5,

ELECTRONIC MUSICAL INSTRUMENTS WITH TONE GENERATING, MIXING, AND. DISTRIBUTING SYSTEMS Original Filed Jan. 25, 1965 s Sheets-Sheet 6 HPSMO 0/! RH N/KH H/lrl) HAL V00 ATTORNEYS United States Patent US. Cl. 841.01 12 Claims ABSTRACT OF THE DISCLOSURE In an electronic musical instrument of the keyboard type, comprising:

(1) a generator system having at least twelve series of signal sources,

(2) a keyswitch system having at least twelve series of keyswitches which are capable of switching on tone signals corresponding to depressed keys,

(3) an output system, and

(4) a signal distributing system which is coupled between said generator system and said keyswitch system and which includes at least twelve mixing networks,

each of said at least twelve mixing networks is coupled between each of said at least twelve series of signal sources and each of said at least twelve series of keyswitches, and has an even number of impedance elements connected in series in such a way that a bottom terminal, junction points in an even order from said bottom terminal and a top terminal of said even number of impedance elements are connected to keyswitches of each of said at least twelve series of keyswitches, respectively, and further in such a 'way that junction points in an odd order from said bottom terminal are connected to signal sources of each of said at least twelve series of signal sources, respectively, and produces a series of composite tone signals corresponding to said keyswitches of each of said at least twelve series of keyswitches. Said series of composite tone signals have sub-octave signals, of which the amplitude percent level shows a progressive increasement from zero percent level to 100 percent level as said composite tone signals ascend in octave with octave ascents of said keyswitches, said increasement being characterized in that said increasement proceeds stepwise and has the first step not more in the increasement than 20 percent and each successive step not less in the increasement than the previous step.

CROSS-REFERENCES TO RELATED APPLICATIONS This application is a continuation application of our US. patent application Ser. No. 427,621 filed on Jan. 25, 1965, now abandoned.

BACKGROUND OF THE INVENTION Field of the invention This invention relates generally to a keyboard type electronic musical instrument and more particularly to a novel signal distributing system for an electronic musical instrument, in which novel composite tone signals can 'be produced by mixing signals generated by signal sources through a mixing network, said composite tone signals corresponding to tones of the musical scale.

The composite tone signal referred to herein is defined as a tone signal which is a mixed tone signal produced by mixing signals in octave relation through a mixing network, and which includes a fundamental signal corresponding to a depressed key as well as a sub-octave signal lower in pitch by one octave than the fundamental signal. Such a composite tone signal is capable of producing a sound having sub-octave pitch, fundamental pitch or both pitches according to the amplitude ratio of the fundamental signal to the sub-octave signal, and making the octave-number of signal sources to be less than the octave-number of keys of the keyboard.

Description of the prior art A conventional electronic musical instrument is usually provided with the same octave-number of tone generators as that of keys of the keyboard for the purpose of distributing tones of the musical scale to each key as shown, for example, in US. Pat. No. 2,545,665, and consequently is apt to be very expensive.

SUMMARY OF THE INVENTION It is an object of the invention to provide an electronic musical instrument having a novel signal distributing system capable of distributing signals to a greater number of keyswitches corresponding to keys of the keyboard in octave-number than that of said signals, by employing novel composite tone signals.

It is another object of the invention to provide an electronic musical instrument having a novel signal distributing system and two kinds of difference signal generators instead of frequency dividers in low frequency range, said signal distributing system distributing signals which include difference signals generated by said two kinds of difference signal generators, to a greater number of keyswitches in octave-number than that of said signals, by employing novel composite tone signals.

The difference signal referred to hereina'bove is defined as a signal which is produced by mixing two signals derived from signal sources and which has the difference frequency of two frequencies of said two signals, and the difference signal generator is defined as a kind of generator that is capable of producing a difference signal.

There are other objects and particularities of the invention, which will be made obvious from the following detailed description of the invention, with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 9 is a diagram showing the distribution of the A tone signals produced by the system in FIG. 8.

DESCRIPTION OF THE PREFERRED EMBODIMENTS We have discovered a theory that in the human sensation of hearing a recognition with respect to separation of two tones in one octave interval changes with whether pitches of the two tones in an octave interval are in a high frequency range or low frequency range and whether the amplitude of the sub-octave tone is large or small relatively to the amplitude of the fundamental tone.

According to the above theory, when said sub-octave tone is small in amplitude relatively to said fundamental tone, e.g. relative amplitudes of said sub-octave tone and said fundamental tone are 20% :80%, and said two tones are in low frequency range e.g. between 50 Hz. to 200 Hz., man perceives two tones separately. However, man can not perceive two tones but one combined tone having a pitch of sub-octave tone, when said suboctave tone is very small in amplitude with relation to said fundamental tone e.g. %:90% and said two tones are high in pitch, e.g. between 800 Hz. to 3200 Hz.

An electronic musical instrument according to the invention comprises:

(1) a generator system having at least twelve series of signal sources for generating signals of pitches corresponding to the musical scale, each of said at least twelve series of sign-a1 sources being in an arrangement of octave relation to each other,

(2) a keyswitch system having at least twelve series of keyswitches which are capable of switching on tone signals corresponding to depressed keys, each of said at least twelve series of keyswitches being in an arrangement of octavere ation to each other,

(3) an output system which is coupled to said keyswitch system and which includes an amplifier and an electroacoustic translating means, and

(4) a signal distributing system which is coupled between said generator system and said keyswitch system and 'which includes at least twelve mixing networks.

Each of said at least twelve mixing networks is coup ed between each of said at least twelve series of signal sources and each of said at least twelve series of keyswitches.

Each of said at least twelve mixing networks has an even number of impedance elements connected in series in such a way that a bottom terminal, junction points in an even order from said bottom terminal and a top terminal of said even number of impedance elements are connected to keyswitches of each of said at least twelve series of keyswitches, respectively, and further in such a way that junction points in an odd order from said bottom terminal are connected to signal sources of each of said at least twelve series of signal sources, respectively.

Each of said at least twelve mixing networks produces a series of composite tone signals corresponding to said keyswitches of each of at least twelve series of keyswitches in accordance with the invention. Such a series of composite tone signals have sub-octave signals, of which the amplitude percent level shows a progressive increase from zero percent level to 100 percent level as said cornposite tone signals ascend in octave with octave ascents of keyswitches.

Said increase proceeds stepwise and has the first step not more in the increase than percent and each successive step not less in the increase than the previous step. Such a construction can make the octave-number of signal sources to be less than the octave-number of keys of the keyboard.

Following description will explain more details of the invention with reference to accompanying drawings.

The number of various components described hereinafter will be reduced for convenience. For example, the number of signal sources such as oscillators and the successive frequency dividers, the number of mixing networks and keyswitches have been reduced as will be described hereinafter. As the practical matter, of course, the number of series of signal sources should be at least twelve so as to ensure a complete musical scale comprising musical notes C, Clt, D, Dlt, E, F, Fit, G, Git, A, Alt and B. The number of signal sources in each series, the number of mixing networks and keyswitches vary with the type and the size of an electronic musical instrument. Therefore, the explanations set forth hereinafter will be limited to certain characteristic parts of the electronic musical instrument. The other parts will be easily under- 4 stood by referring to the explanation of the certain characteristic parts.

The following description will be made with an electronic instrument using a frequency divider system as an example. The description is also applicable to electronic musical instruments employing a separate oscillator system having separate oscillators for generating each of signals, respectively.

Amplitude percents and impedance values will be hereinafter expressed as illustrative and should not be construed as limitative.

Referring now to FIG. 1 showing the principle of the signal distributing system according to the invention, a generator system comprises a series of five signal sources such as an oscillator 16 and frequency dividers 17, 18, 19 and 20. A signal derived from said oscillator 16 is successively divided by a factor of two by means of the successive frequency dividers 17, 18, 19 and 20. Said oscillator 16 and said frequency dividers 17, 18, 19 and 20 generate five signals in octave relation to each other. These five signals are mixed and delivered to six keyswitches 31, 32, 33, 34, 35 and 36, which are in octave relation to each other, through a mixing network having ten impedance elements in a series connection, i.e. resistors 21, 22, 23, 24, 25, 26, 27, 28, 29 and 30.

The mixed signals are fed to a keyswitch system composed of a series of normally open keyswitches 31, 32, 33, 34, 35 and 36. Said keyswitches 31, 32, 33, 34, 35 and 36 are single-pole keyswitches and are actuated to switch on tone signa s by depressing keys to keyboards (not shown). Tone signals from said keyswitches 31, 32, 33, 34, 35 and 36 are fed to an output system (not shown) which is coupled to said keyswitch system and which includes an amplifier and an electro-acousitc translating means, for the purpose of obtaining the acoustic tones having desired tone colors.

Each of frequency relations between said signals generated by a series of signal sources, i.e., the oscillator 16 and the frequency dividers 17, 18, 19 and 20 is in octave re ation, and frequencies of said signals will be indicated by frequencies of 16f, 8 4], 2f and respectively, for an easy understanding of this invention.

Key positions on the keyboard corresponding to the six keyswitches 31, 32, 33, 34, 35 and 36 are arranged in octave relation to each other. A key position corresponding to the keyswitch 35 is higher, on the keyboard, by one octave than that corresponding to the keyswitch 36. A key position corresponding to the keyswitch 34 is higher, on the keyboard, by one octave than that corresponding to the keyswitch 35 and so on. Therefore, an octave ascent of the key positions on the keyboard corresponds to an octave ascent of the keyswitches from the lowest keyswitch 36 through keyswitches 35, 34, 33 and 32 to the highest keyswitch 31.

The mixing network is constituted by even number of impedance elements in a series connection, i.e. the ten resistors 21, 22, 23, 24, 25, 26, 27, 2'8, 29 and 30 in a series connection.

A bottom terminal 11, junction points 2, 4, 6 and 8 in an even order from said bottom terminal 11 and the top terminal 10 of said series connection are connected to said series of keyswitches 36, 35, 34, 33, 32 and 31, respectively. Junction points 1, 3, 5, 7 and 9 in an odd order from said bottom terminal 11 are connected to said series of signal sources, i.e. frequency dividers 20, 19, 18 and 17 and the oscillator 16, respective y.

Consequently, five signals of five signal sources, i.e. the frequency dividers 20, 19, 18 and 17 and the oscillator 16, are delivered to the six keyswitches 36, 35, 34, 33, 32 and 31 in octave relation to each other by the mixing network comprising a series connection of said ten resistors, so as to form six composite tone signals corresponding to said six keyswitches 36, 35, 34, 33, 32 and 31.

Resistors 21, 23, 25, 27 and 29 in an odd order from the top of said series connection have resistance values of, for example, 1.00R (ohm), 1.82R (ohm), 2.50R (ohm), 4.00R (ohm) and 10.0R (ohm) respectively, and form signal paths through which signals from the oscillator 16 and dividers 17, 18, 19 and are fed to the keyswitches 31, 32, 33, 34 and 35 so as to form sub-octave signals shown as, for example, SUB 100%, SUB 55%, SUB 40%, SUB and SUB 10%, respectively, in FIG. 1

The sub-octave signals defined hereinbefore will be used hereinafter for designating signals lower in pitch by one octave than fundamental signals, respectively. The resistors 22, 24, 26, 28 and in an even order from the top end of said series connection have resistance values of, for example, 2.22R (ohm), 1.67R (ohm), 1.33R (ohm), 1.11R (ohm), and 1.00R (ohm) respectively, and form signal paths through which signals of the oscillator 16 and dividers 17, 18, 19 and 20 are fed to the keyswitches 32, 33, 34, and 36 so as to form fundamental signals shown as, for example, FUND FUND 60%, FUND 75%, FUND 90%, FUND 100%. As the practical matter, of course, the impedance values, i.e. the resistance values are inversely proportional to amplitude levels of signals fed to the keyswitches.

A signal generated by the oscillator 16 having frequency 16 Hz. in an actual frequency range of, for example, 800 Hz. to 3200 Hz., is fed to the keyswitch 31 through the resistor 21 in a mixing ratio 0:100 with respect to amplitude as indicated by FUND 0% and SUB 100% of FIG. 1 and forms a composite tone signal having no fundamental signal and only a sub-octave signal of 100% amplitude.

A signal generated by the oscillator 16 having frequency 16f Hz. and a signal generated by the frequency divider 17 having frequency 8 Hz., in actual frequency range of, for example, 400 Hz. to 1600 Hz., are mixed through the mixing resistors 22 and 23 in a mixing ratio of about 45:55 with respect to their amplitude, respectively, as indicated by FUND 45% and SUB of FIG. 1 and are fed to the keyswitch 32 so as to form another composite tone signal having a fundamental signal of 45 amplitude and a sub-octave signal of 55% amplitude.

A signal generated by the frequency divider 17 having frequency 8 Hz. and a signal generated by the frequency divider 18 having frequency 4 Hz. in actual frequency range of, for example, 200 Hz. to 800 Hz., are mixed through the mixing resistors 24 and 25 in a mixing ratio of about :40 with respect to their amplitude, respectively, as indicated by FUND 60% and SUB 40% in FIG. 1, and are fed to the keyswitch 33 so as to form a composite tone signal having a fundamental signal of 60% amplitude and a sub-octave signal of 40% amplitude.

A signal generated by the frequency divider 18 having frequency 4 Hz. and a signal generated by the frequency divider 19 having frequency 2 Hz., in actual frequency range of, for example, 100 Hz. to 400 Hz., are mixed through the mixing resistors 26 and 27 in a mixing ratio of about 75:25 with respect to their amplitude, respectively, as indicated by FUND 75% and SUB 25% in FIG. 1, and are fed to the keyswitch 34 so as to form a composite tone signal having a fundamental signal of 75% amplitude and a sub-octave signal of 25% amplitude.

A signal generated by the frequency divider 19 having a frequency 2 Hz. and a signal generated by the frequency divider 20 having a frequency 1 Hz. in actual frequency range of, for example, 50 Hz. to 200 Hz., are mixed through the mixing resistors 28 and 29 in a mixing ratio of about 90: 10 with respect to their amplitude, respectively, as indicated by FUND 90% and SUB 10% in FIG. 1, and are fed to the keyswitch 35 so as to form a composite tone signal having a fundamental signal of 90% amplitude and a sub-octave signal of 10% amplitude.

A signal generated by the frequency divider 20 having a frequency 1 Hz. in an actual frequency range of, for example, '50 Hz. to 200 Hz., is fed to the keyswitch 36 through the resistor 30 in a mixing ratio 100:0 with respect to amplitude as indicated by FUND 100% and SUB 0% in FIG. 1, so as to form a composite tone signal having a fundamental signal of 100% amplitude and no sub-octave signal.

Five signals generated by a series of signal sources, i.e. said oscillator 16 and said successive frequency dividers 17, 18, 19 and 20 are distributed to the six keyswitches 31, 32, 33, 34, 35 and 36 through the signal distributing system comprising the mixing network having ten resistors 21, 22, 23, 24, 25, 26, 27, 28, 29 and 30 so as to form six composite tone signals. Therefore, said six composite tone signals make the octave-number of a series of signal sources to be less by one than the octave-number of keyswitches.

From FIG. 1, one can understand easily the following important feature of the invention.

Concerning sub-octave signals, a series of composite tone signals, i.e. composite tone signals of the keyswitches 36, 35, 34, 33, 32 and 31, have sub-octave signals, of which the amplitude level percent shows a progressive increasement from zero percent level to 100 percent level, i.e. 0%, 10%, 25%, 40%, 55% and 100% as said composite tone signals ascend in octave with octave ascents of the keyswitches 36, 35, 34, 33, 32 and 31. An increase from 0% to 100% proceeds stepwise and is characterized in that said increase has the first step of 10% increase not more than 20% increase and each successive step not less in the increase than the previous step.

The principle of the invention described with reference to FIG. 1 will be more clearly explained by referring to FIG. 2. Vertical lines indicate frequencies f, 2f, 4f, 8 and 16 in a real frequency region. A pitch interval between the frequencies f and 2 is one octave, a pitch interval between the frequencies 2f and 4; is one octave, and each of the remaining pitch intervals between frequencies 4 and 8f, 8 and 16f is also one octave. Therefore, there are four octave pitch intervals between the frequencies f and 16 corresponding to the signal sources 20 and 16, respectively.

Reference numerals 601, 602, 603, 604, 605 and 606 indicate the spectra of composite tone signals derived from the keyswitches 31, 32, 33, 34, 35 and 36 shown in FIG. 1, respectively.

The thick vertical lines denote the fundamental components of sub-octave signals and fundamental signals, and thin declining curves denote the envelopes of harmonics of said sub-octave and fundamental signals. The heights of the thick lines denote the amplitudes of the fundamental component of the sub-octave and fundamental signals. A pitch interval sensation between the composite tone signals 606 and 605 is one octave, a pitch interval sensation between the composite tone signals 605 and 604 is one octave, and each of the remaining pitch interval sensations between the composite tone signals 604 and 603, 603 and 602, 602 and 601 is also one octave. Therefore, there are five octaves in pitch interval sensation between the composite tone signals 606 and 601.

The following description will explain the reason why the five octave interval sensation as an auditory stimulus exists between the composite tone signals 606 and 601.

The composite tone signal 606 comprises only a fundamental signal 616 having a 100% ampltiude and a frequency f, and therefore, the pitch sensation of said composite tone signal depends perfectly on the frequency f of said fundamental signal 616.

The composite tone signal 605 comprises a sub-octave signal 614 having a 10% amplitude and a frequency f, and a fundamental signal 615 having a amplitude and a frequency 2 These frequencies f and 2 are in low frequency range, e.g. 50 Hz. to 200 Hz. Therefore, the pitch sensation of said sub-octave signal 614 is extremely weaker than that of said fundamental signal 615 and is almost masked by that of said fundamental signal 615, even though said sub-octave signal 614 is heard as a very weak sub-octave tone lower by one octave in pitch than said fundamental signal 615.

The composite tone signal 604 comprises a sub-octave signal 612 having a 25% amplitude and a frequency 2 and a fundamental signal 613 having a 75% amplitude and frequency 4 These frequencies 2 and 4] are in a little low frequency range, e.g. 100 Hz. to 400 Hz. Therefore, the pitch sensation of said sub-octave signal 612 is weaker than that of said fundamental signal 613. Said sub-octave signal is heard separately as a weak sub-octave tone.

The composite tone signal 603 comprises a sub-octave signal 610 having a 40% amplitude and a frequency 47, and a fundamental signal 611 having a 60% amplitude and a frequency 8 These frequencies 4] and 8 are in middle frequency range, e.g. 200 Hz. to 800 Hz. Therefore, the pitch sensation of said sub-octave signal 610 is a little weaker than that of said fundamental signal 611. Said sub-octave signal 610 is heard vaguely, separately or not separately, as a sub-octave tone.

The composite tone signal 602 comprises a sub-octave signal 608 having a 55% amplitude and a frequency 8 and a fundamental signal 609 having a 45% amplitude and a frequency 16 These frequencies 8 and 16 are in a little high frequency range, e.g. 400 Hz. to 1600 Hz. Therefore, the pitch sensation of said sub-octave signal 608 is slightly stronger than that of said fundamental signal 609 and almost masks that of said fundamental signal 609. Consequently, man perceives only one pitch corresponding to the frequency 8].

The composite tone signal 601 comprises a sub-octave signal 607 having a 100% amplitude and a frequency 16 and therefore, the pitch sensation of said composite tone signal 601 depends perfectly on the frequency 16).

The following description will explain detail of the octave interval sensation between two adjacent composite tone signals, i.e., the composite tone signals 606 and 605, the composite tone signals 605 and 604, the composite tone signals 604 and 603 and so on.

The composite tone signal 606 has, of course, only one pitch sensation corresponding to the frequency On the other hand, with respect to the composite tone signal 605, the fundamental signal 615 has its own pitch corresponding to the frequency 21, because said fundamental signal 615 is very large in amplitude. The sub-octave signal 614, of course, has its own pitch corresponding to the frequency f, and the pitch sensation of this sub-octave signal 614 is extremely weaker than that of said fundamental signal 615. Said sub-octave signal 614 merely acts as a very weak sub-octave tone which is lower in pitch by one octave than the fundamental signal 615. These two pitches are separately distinguished as an auditory stimulus.

Therefore, a comparison of the composite tone signal 606 with the composite tone signal 605 from the standpoint of an auditory stimulus will practically result in a comparison of the fundamental signal 616 having the frequency f with the fundamental signal 615 having the frequency 2 rather than a comparison of the fundamental signal 616 with the sub-octave signal 614 because a very strong pitch sensation produced by the fundamental signal 616 cannot be compared with an extremely weak pitch sensation produced by the sub-octave signal 614. Thus one octave interval sensation is produced between said two composite tone signals 606 and 605.

With respect to the composite tone signals 605 and 604, the sub-octave signals 614 and 612 mixed in the composite tone signals 605 and 604, respectively, also act as weak sub-octave tones which are lower in pitch by one octave than the fundamental signals 615 and 613,

respectively, because the pitch sensations of these suboctave signals 614 and 612 are weaker than those of said fundamental signals 615 and 613, respectively.

When the composite tone signal 605 is compared with the composite tone signal 604 from the standpoint of an auditory stimulus, as a matter of course, man will compare the sub-octave signal 614 having the frequency f with the sub-octave signal 612 having the frequency 21'' in an octave relation to each other and also compare the fundamental signal 615 having the frequency 2 with the fundamental signal 613 having the frequency 4 in an octave relation to each other. Therefore, one octane interval sensation is produced between said two composite tone signals 605 and 604.

With respect to the composite tone signals 604 and 603, the sub-octave signals 612 and 610 mixed in the composite tone signals 604 and 603, respectively, can be perceived as sub-octave tones which are lower in pitch by one octave than the fundamental signals 613 and 611 and also be perceived as if they were the fundamental tones of said composite tone signals 604 and 603, respectively, although the amplitudes of the sub-octave signals 612 and 610 are smaller than those of the fundamental signals 613 and 611, respectively.

In general, the higher the frequency range of signals is raised, the more predominantly the sub-octave signal acts as if it were a fundamental tone rather than acts as a sub-octave tone, as an auditory stimulus.

At any case when the composite tone signal 604 is compared with the composite tone signal 603 from the standpoint of an auditory stimulus, as a matter of course, man will compare the sub-octave signal 612 having the frequency 2 with the sub-octave signal 610 having the frequency 4 in an octave relation to each other and also compare the fundamental signal 613 having the frequency 4 with the fundamental signal 611 having the frequency 8 in an octave relation to each other. Therefore, one octave interval sensation is produced between said two composite tone signals 604 and 603.

With respect to the composite tone signals 60.3 and 602, the sub-octave signals 610- and 608 mixed in the composite tone signals 603 and 602, respectively, can be perceived basically as sub-octave tones which are lower in pitch by one octave than the fundamental signal 611 and the fundamental signal 609, and can be perceived as if they were the fundamental tones of the composite tone signals 603 and 602, respectively, although, with respect to the composite tone signal 603, an amplitude of the sub-octave signal 610 is smaller than that of the fundamental signal 611.

When the composite tone signal 603 is compared with the composite tone signal 602 from the standpoint of an auditory stimulus, as a matter of course, man will compare the sub-octave signal 610 having the frequency 4f with the sub-octave signal 608 having the frequency 8f in an octave relation to each other and also compare the fundamental signal 611 having the frequency 8 with the fundamental signal 609 having the frequency 161 in an octave relation to each other. Therefore, one octave interval sensation is produced between said two composite tone signals 603 and 602.

With respect to the composite tone signal 602, the fundamental signal 609 corresponding to the frequency 16f is almost masked by the upper harmonics of the sub-octave signal 608 corresponding to the frequency 8f.

In general, a signal generated by an oscillator or a frequency divider contains a plurality of upper harmonics which gradually decrease in the amplitude with an ascent of harmonic order.

Therefore, said fundamental signal 609 acts as an upper harmonics of said sub-octave signal 608, because said fundamental signal 609 is high in pitch and smaller in amplitude than said sub-octave signal 608. Even when said fundamental signal 609 has its own pitch sensation, the pitch sensation of said sub-octave signal 608 is stronger than that of said fundamental signal 609. Consequently, the composite tone signal 602 has a pitch of said sub-octave signal 608 corresponding to the frequency 8].

On the other hand, the composite tone signal 601 comprises only one sub-octave signal 607 and has, of course, only one pitch sensation corresponding to the frequency 16 Therefore, a comparison of the composite tone signal 602 with the composite tone signal 601 from the standpoint of an auditory stimulus, will practically result in a comparison of the sub-octave signal 608 having the frequency 8 with the sub-octave signal 607 having the frequency 16 rather than a comparison of the fundamental signal 609 having the frequency 16f with the sub-octave signal 607 having the frequency 16 Thus, one octave interval sensation is produced between said composite tone signals 602 and 601.

Consequently, man perceives one octave interval sensation betwen the two adjacent composite tone signals 606 and 605 and perceives one octave interval sensation be tween the two adjacent composite tone signals 605 and 604, and also perceives one octave interval sensation between each two adjacent composite tone signals, i.e., the composite tone signals 604 and 603, the composite signals 603 and 602, and the composite tone signals 602 and 601.

As a result, man perceives as if there were a five octave interval as an auditory stimulus in the range from the composite tone signals 606 through the composite tone signals 605, 604, 603 and 602 to the composite tone signal 601, but really there is a four octave interval in the real frequency region of signal sources in the range from the frequency 1 corresponding to the frequency divider 20 through the frequencies 2 4 and 8f corresponding to the frequency dividers 19, 18 and 17 respectively, to the frequency 16 corresponding to the oscillator 16.

Consequently, five signals, in octave relation to each other, generated by a series of signal sources such as the oscillator 16 and the succesive four frequency dividers 17, 18, 19 and 20 are distributed to a series of six keyswitches 31, 32, 33, 34, 35 and 36, in octave relation to each other, by the mixing network having the ten resistors 21, 22, 23, 24, 25, 26, 27, 28, 29 and 30 in a series connection. In other words, said mixing network produces a series of six different composite tone signals corresponding to said series of six keyswitches 31, 32, 33, 34, 35 and 36 in accordance with the invention.

It has been explained above that each two adjacent composite tone signals of a series of keyswitches maintains a sensation of one octave interval. In the interval from the lowest composite tone signal 606 derived by the keyswitch 36 to the highest composite tone signal 601 derived by the keyswitch 31, there is a five octave interval at the keys on keyboard, although actual frequencies of signal sources have a four octave interval. It is difficult, however, for human ear to recognize whether the musical interval widely spread over three octave interval, four octave interval, five octave interval, or six octave interval is an actual frequency. Therefore, as a practical matter the novel composite tone signals according to the invention give no disadvantage to the musical playing.

It is preferable for realizing the novel scope of the invention that signals generated by signal sources contain many upper harmonics. In a case wherein two signals in an octave relation to each other are mixed together so as to form a composite tone signal according to the invention, if each of said two signals contains no upper harmonics, different mixing ratios of said two signals not only cause the changes of pitch sensation of said composite tone signal, but also cause great changes in tone color of said composite tone signal. For example, if signals generated by the oscillator 16 and the frequency divider 17 are of sine waveform having no upper harmonics, while a composite tone signal derived from the keyswitch 32 contains the second harmonics, while a composite tone signal derived from the keyswitch 31 does not contain the second harmonics. Therefore, there exists a difference in tone color between two composite tone signals derived from the keyswitches 31 and 32. In practice, each of the signals generated by the oscillator 16, and the frequency dividers 17, 18, 19 and 20 contains many upper harmonics. Therefore, said different mixing ratios cause the changes of said pitch sensation, but do not cause the great changes of said tone color by means of sufiicient upper harmonics.

Referring to FIG. 3 showing an embodiment of the signal distributing system provided with two representative mixing networks for producing two representative series of composite tone signals according to the invention, a generator system comprises twelve series of signal sources such as oscillators and successive frequency dividers. The following description illustrates representatively an arrangement for C series of composite tone signals among six series of composite tone signals, namely C, B, All, A, Gil and G series of composite tone signals, and another arrangement of Fit series of composite tone signals among six series of composite tone signals, namely Flt, F, E, Di, D and Cit series of composite tone signals.

A signal derived from an oscillator 37 is successively divided by a factor of two by means of the successive frequency dividers 38, 39, 40 and 41. A signal derived from an oscilator 42 is successivly divided by a factor of two by means of successive frequency dividers 43, 44 and 45.

C series of five signal sources comprises the oscillator 37 and frequency dividers 38, 39, 40 and 41, and generate C series of five signals in octave relation to each other. These five signals are distributed to C series of six keyswitches 62, 64, 66, 68, 70 and 72 which are in octave relation to each other, through a mixing network which comprises a series connection of eight impedance elements, i.e. a high pass filter 46 and resistors 48, 49, 52, 53, 56, 57 and 59 and another resistor 61.

While Fit series of four signal sources comprise the oscillator 42 and frequency dividers 43, 44 and 45, and generate Fit series of four signals in octave relation to each other. These four signals are distributed to F series of five keyswitches 63, 65, 67, 69 and 71 which are in octave relation to each other, through a mixing network which comprises a series connection of six impedance elements, i.e. a high pass filter 47 and resistors 50, 51, 54, 55 and 58 and another resistor 60.

The following description will explain the distribution of C series of signals.

A signal generated by the oscillator 37 is fed to the keyswitch 62 through the high pass filter 46 enriching upper harmonics in a mixing ratio 0:100 with respect to amplitude as indicated by FUND 0% and SUB in FIG. 3 and forms a composite tone signal having only suboctave signal and no fundamental signal according to the invention.

A signal generated by the oscillator 37 and a signal generated by the frequency divider 38 are mixed through the mixing resistors 48 and 49 in a mixing ratio of about 30:70 with respect to their amplitude, respectively, as indicated by FUND 30% and SUB 70% in FIG. 3 and are fed to the keyswitch 64 so as to form another composite tone signal having a fundamental signal of 30% amplitude and a sub-octave signal of 70% amplitude according to the invention.

A signal generated by the frequency divider 38 and a signal generated by the frequency divider 39 are mixed through the mixing resistors 52 and 53 in a mixing ratio of about 60:40 with respect to their amplitude, respectively, as indicated by FUND 60% and SUB 40% in 11 FIG. 3 and are fed to the keyswitch 66 so as to form a composite tone signal having a fundamental signal of 60% amplitude and a sub-octave signal of 40% amplitude according to the invention.

A signal generated by the frequency divider 39 and a signal generated by the frequency divider 40 are mixed through the mixing resistors 56 and 57 in a mixing ratio of about 90:10 with respect to their amplitude, respectively, as indicated by FUND 90% and SUB 10% in FIG. 3 and are fed to the keyswitch 68 so as to form a compositie tone signal having a fundamental signal of 90% amplitude and a sub-octave signal of 10% amplitude according to the invention.

A signal generated by the frequency divider 40 is fed to the keyswitch 70 through the resistor 59 in a mixing ratio of 100:0 with respect to the amplitude as indicated by FUND 100% and SUB in FIG. 3 and forms a composite tone signal having only fundamental signal and no sub-octave signal according to the invention.

Five signals generated by signal sources, that is, the oscillator 37 and the successive frequency dividers 38, 39, 40 and 41 are distributed to the six keyswitches 62, 64, 66, 68, 70 and 72 through the mixing network comprising a series connection of eight impedance elements, i.e. the high pass filter 46 and resistors 48, 49, 52, 53, 56, 57 and 59 and another resistor 61 so as to form six composite tone signals. Therefore, the number of signal sources is less than that of keyswitches.

Man perceives, naturally, one octave interval between the two composite tone signals derived from the keyswitches 72 and 70, because said two composite tone signals are prepared similarly in a conventional manner.

In a similar way to that described with FIG. 1, man perceives one octave interval between the two composite tone signals derived from the keyswitches 70 and 68 and also perceives one octave interval between each two composite tone signals, i.e., the composite tone signals derived from the keyswitches 68 and 66, the composite tone signals derived from the keyswitches 66 and 64, and the composite tone signals derived from the keyswitches 64 and 62.

As a result, man perceives as if there were a five octave interval as an auditory stimulus in the range from the composite tone signal derived from the keyswitch 72, through the composite tone signals derived from the keyswitches 70, 68, 66 and 64, to the composite tone signal derived from the keyswitch 62. According to the above illustration the other five series of signals generated by the signal sources 37, 38, 39 and 40 as one group namely B, At, A, Gt, and G series of signal sources, produce five series of composite tone signals which are fed to the corresponding keyswitches, respectively, in the same manner as that mentioned about C series of signal sources.

The following description will explain the distribution of Fit series of signals.

A signal generated by the oscillator 42 is fed to the keyswitch 63 through the high pass filter 47 enriching upper harmonics in a mixing ratio 0:100 with respect to an amplitude as indicated by FUND 0% and SUB 100% in FIG. 3 and forms a composite tone signal having only sub-octave signal and no fundamental signal according to the invention.

A signal generated by the oscillator 42 and a signal generated by the frequency divider 43 are mixed through the mixing resistors 50 and 51 in a mixing ratio about 40:60 with respect to their amplitude, respectively, as indicated by FUND 40% and SUB 60% in FIG. 3 and are fed to the keyswitch 65 so as to form a composite tone signal having a fundamental signal of 40% and a sub-octave signal of 60% amplitude according to the invention.

A signal generated by the frequency divider 43 and a signal generated by the frequency divider 44 are mixed through the mixing resistors 54 and 55 in a mixing ratio about 80:20 with respect to their amplitude, respectively, as indicated by FUND 80% and SUB 20% in FIG. 3 and are fed to the keyswitch 67 so as to form a composite tone signal having a fundamental signal of 80% amplitude and a sub-octave signal of 20% amplitude according to the invention.

A signal generated by the frequency divider 44 is fed to the keyswitch 69 through the resistor 58 in a mixing ratio 100:0 with respect to the amplitude as indicated by FUND 100% and SUB 0% in FIG. 3 and forms a composite tone signal having only fundamental signal and no sub-octave signal according to the invention.

A signal generated by the frequency divider is fed to the keyswitch 71 through the resistor 60 in a mixing ratio 100:0 with respect to the amplitude as indicated by FUND 100% and SUB 0% in FIG. 3 and forms a composite tone signal having only fundamental signal and no sub-octave signal according to the invention.

Four signals generated by signal sources, that is, the oscillator 42 and the successive frequency dividers 43, 44 and 45 are distributed to five keyswitches 63, 65, 67, 69 and 71 through the mixing network comprising a series connection of six impedance elements, i.e. the high pass filter 47 and resistors 50, 51, 54, and 58 and another resistor so as to form five composite tone signals. Therefore, the number of signal sources is less than that of keyswitches.

Naturally, man perceives one octave interval between the two composite tone signals derived from the keyswitches 71 and 69.

In a similar manner to that described relative to FIG. 1 man perceives one octave interval between the two composite tone signals derived from the keyswitches 69 and 67, and also perceives one octave interval between each two composite tone signals, i.e., the composite tone signals derived from the keyswitches 67 and and the composite tone signals derived from the keyswitches 65 and 63.

As a result, man perceives as if there were a four octave interval as an auditory stimulus in the range from the composite tone signals derived from the keyswitch 71, through the composite tone signals derived from the keyswitches 69, 67 and 65, to the composite tone signal derived from the keyswitch 63.

According to the above illustration, the other five series of signals generated by the signal sources 42, 43, 44 and 45 as one group namely F, E, Di, D and Cit series of signal sources, produce five series of composite tone signals, namely F, E, D3, D and Cit series of composite tone signals which are fed to the corresponding keyswitches, respectively, in the same manner as that mentioned about Fit series of signal sources,

From FIG. 3 one can understand easily the following important scope of the invention.

With respect to C series of composite tone signals, the amplitudes of sub-octave signals increase progressively from zero percent level to 100 percent level, i.e. 0%, 0%, 10%, 40%, 70% and as composite tone signals ascend in octave with octave ascents of keyswitches 72, 70, 68, 66, 64 and 62. The increase from 0% to 100% proceeds stepwise and is characterized in that said increase has the first step of 10% increase which is not more than 20% and each successive step not less in the increase than the previous step.

With respect to Fit series of composite tone signals, the amplitudes of sub-octave signals increase progressively from zero percent level to 100 percent level, i.e. 0%, 0%, 20%, 60% and 100%, as composite tone signals ascend in octave with octave ascents of keyswitches, 71, 69, 67, 65 and 63. The increase from 0% to 100% proceeds stepwise and is characterized in that an increase has the first step of 20% increase which is not more than 20% and each successive step not less in the increase than the previous step.

The construction illustrated in FIG. 3 has a feature that when the composite tone signals corresponding to the musical scale are performed one after another from the highest tone to the lowest tone and from the lowest to the highest, man perceives a natural musical interval sensation between respective composite tone signals without a sudden change in tone quality. Consequently, man perceives successive and natural tones of five octaves corresponding to the musical scale at keys on the keyboard in spite of only four octaves in the frequency range of signal sources including oscillators and frequency dividers.

In the arrangement shown in FIG. 3, the twelve series of signal sources are divided into two groups, such as a group of C, B, Ail, A, G1? and G series of signal sources and a group of Fit, F, E, Di, D and Cit series of signal sources. Said twelve series can be divided into groups more than two, so that tone quality of successive composite tone signals corresponding to the musical scale at keys may change more smoothly with a variation in a mixing ratio of a sub-octave signal to a fundamental signal.

The amplitude percent levels of fundamental signals and sub-octave signals shown in FIGS. 1, 2 and 3 are mere examples of percent levels.

With relation to the increments of amplitude percent levels of sub-octave signals with octave ascents of keyswitches shown in FIG. 1 and FIG. 3, said increments have the first steps of the increments from level. One of said first steps is 10% which is not more in the increment than 20% as shown in FIG. 1. The other of said first steps is also 10% which is not more in the increment than 20% as shown with C series of composite tone signals in FIG. 3. The other one of said first steps is 20% not more in the increment than 20% as shown with Flt series of composite tone signals in FIG. 3.

It is desirable that the first step of the increment of amplitude percent level of sub-octave signal is as small as possible.

As a practical matter, however, it is adequate that the first step is of an about step. The first step more than 20% step makes it impossible to keep one octave interval sensation between a composite tone signal having no suboctave signal and a composite tone signal having a suboctave signal of amplitude percent level more than 20% and prevents the formation of novel composite tone signals according to the invention.

Referring to FIG. 4, a mixing network further includes additional impedance elements i.e. additional resistors 73, 74, 75 and 76. An Oscillator 16, four frequency dividers 17, 18, 19 and 20 and resistors 21, 22, 23, 24, 25, 26, 27, 28, 29 and 30 are the same as those of the circuit in FIG. 1, respectively, although resistance values of said resistors 21, 22, 23, 24, 25, 26, 27, 28, 29 and 30 are a little modified in accordance with the addition of said additional resistors 73, 74, 75 and 76. Novel composite tone signals are produced in a way similar to that of FIG. 1. Upper harmonics of the composite tone signals can be enriched by supplying keyswitches 33, 34, 35 and 36, through the additional resistors 73, 74, 75 and 76, with additional signals generated by the oscillator 16 and frequency dividers 17, 18 and 19 in appropriate amplitude, respectively. Composite tone signals derived from the keyswitches 33, 34, 35 and 36 are not interrupted by said additional signals mixed in said composite tone signals through the additional resistors 73, 74, 75 and 76, respectively and can be improved in the upper harmonics.

On the other hand, composite tone signals derived from the highest two keyswitches 31 and 32 are, generally, high in pitch. Even if they had upper harmonics in a high frequency range, said high upper harmonics would not be heard sufficiently because of the limitation of human audible frequency range as well as the limitation of frequency characteristics of the output system including an amplifier and a electroacoustic translating means.

Consequently, all composite tone signals derived from the keyswitches 31, 32, 33, 34, 35 and 36 have satisfactory upper harmonics and are much alike in tone color because of their satisfactory upper harmonics.

Referring to FIG. 5 showing another distributing system of signals generated by a series of signal sources according to the invention, six signals generated by six signal sources in octave relation to each other such as an oscillator 81 and frequency dividers 82, 83, 84 and 85 and 86 are distributed through a mixing network having impedance elements, i.e. resistors 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103 and 104 to eight keyswitches 105, 1-06, 107, 108, 109, 111, and 112 in octave relation to each other. Consequently, said six signals form a series of eight composite tone signals corresponding to said eight keyswitches. There exists one octave interval sensation between any two adjacent tones thereof.

The mixing network has an even number of impedance elements in a series connection, i.e. twelve resistors 93, 87, 94, 88, 95, 89, 96, 90, 97, 91, 98 and 92 in a series connection. A bottom terminal 213, even order junction points 202, 204, 206, 208, and 210 from said bottom terminal 213 and a top termnial 212 of said series connection of twelve resistors are connected to a series of keyswitches 112, 111, 110, 109, 108, 107, and 106, respectively. Junction points in an odd order from the bottom terminal 213 of said twelve resistors in series connection are connected to a series of signal sources such as the frequency dividers 86, 85, 84, 83 and 82 and the oscillator 81, respectively.

The mixing network has also further impedance elements, i.e. resistors 104, 103, 102, 101, 100 and 99, which are connected in such a way that junction points 201, 203, 205, 207 and 209 in an odd order are connected through further resistors 104, 103, 102, 101 and 100 to junction points 204, 206, 208, 210 and 212 in the even order after the next even order, respectively, and the last junction point 211 in an odd order is connected through a further resistor 99 to an additional keyswitch 105.

Signals generated by the oscillator 81 and the frequency divider 82, 83, 84, 85 and 86 are distributed to the keyswitches 107, 108, 109, 110, 111 and 112 through the resistors 87, 88, 89, 90, 91 and 92, respectively, and act as fundamental signals of composite tone signals derived from respective keyswitches.

Signals generated by said oscillator 81 and said frequency divider 82, 83, 84, 85 and 86 are distributed to the keyswitches 106, 107, 108, 109, 110 and 111 through the resistors 93, 94, 95, 96, 97 and 98, respectively, and act as sub-octave signals of composite tone signals derived from respective keyswitches.

Signals generated by said oscillator 81 and said frequency dividers 82, 83, '84, 85 and 86 are distributed to the keyswitches 105, 106, 107, 108, 109 and 110 through the resistors 99, 100, 101, 102, 103 and 104, respectively, and act as double-sub-octave signals of composite tone signals which are lower in pitch by two octaves than the fundamental signals.

A series of eight composite tone signals derived from keyswitches 112, 111, 110, 109, 108, 10-7, 106 and 105 have double-snb-octave signals, of which the amplitude percent level shows a progressive increasement from zero level to 100 percent level as said eight composite tone signals ascend in octave with octave ascents of said keyswitches.

Said increase is characterized in that said increase proceeds stepwise and has the first step not more than 20 percent and each successive step not less in the increasement than the previous step. Said a series of eight composite tone signals also have sub-octave signals, of which the amplitude level percent shows a progressive increasement from zero level as said eight composite tone signals ascend in octave with octave ascents of said keyswitches.

Said increase is characterized in that said increase proceeds stepwise and has the first step not more in the increase than 20 percent.

The mixing ratio of a double-sub-octave signal to a sub-octave signal to a fundamental signal in a series of said composite tone signals will be arranged easi y in a way similar to that of FIGS. 1 and 3 in accordance with the invention.

Therefore, people perceive a seven octaves interval sensation from the composite tone signal derived by the keyswitch 112 to the composite tone signal derived by the keyswitch 105 on the keyboard, but there is a five octaves interval from the signal generated by the frequency divider 86 to the signal generated by the oscillator 81 in actual frequency range.

The above illustration explains about only one series of composite tone signals in octave relation to each other. and will be useful for constructing the other eleven series of composite tone signals in octave relation to each other.

The principle of the invention described hereinbefore may also be embodied in an electronic musical instrument having two manual keyboard, as shown in FIG. 6 and FIG. 7.

Referring to FIG. 6 showing a distribution of one representative series of signals in a two manual keyboard type electronic musical instrument, keyswitches 115, 116, 117 and 118 are actuated by respective keys (not shown) in octave relation to each other in the upper manual keyboard 113, and keyswitches 119, 120, 121 and 133 are actuated by respective keys (not shown) in octave relation to each other in the lower manual keyboard 114.

According to the principle of the invention, four signals generated by a series of signal sources such as an oscillator 123 and frequency dividers 124, 125 and 126 are distributed, through a mixing network having a series connection of eight impedance elements, i.e. resistors 16], 162, 163, 164, 165, 166, 167 and 168, to five keyswitches 115, 116, 117, 118 and 122 in octave relation to each other so as to form a series of five composite tone signals having one octave interval sensation between any two adjacent thereof.

The keyswitch 119 switches on the same composite tone signal as that switched by the keyswitch 116. Similarly, the keyswitch 120 switches on the same composite tone signal as that switched by the keyswitch 117, and the keyswitch 121 switches on the same composite tone signal as that switched by the keyswitch 118.

Therefore, higher four composite tone signal, higher in pitch, of a series of five composite tone signals constructed of said four signals of signal sources, are switched on by keyswitches 115, 116, 117 and 118 in the upper manual keyboard 113. Lower four composite tone signals, lower in pitch, of said series of five composite tone signals, are switched on by keyswitches 119, 120, 121 and 122 in the lower manual keyboard 114.

Referring to FIG. 7 showing another distribution of one representative series of signals in a two manual keyboard type electronic musical instrument, keyswitches 129, 130, 131 and 132 are actuated by respective keys (not shown) in octave relation to each other in the upper manual keyboard 127, and keyswitches 133, 134, 135 and 136 are actuated by respective keys (not shown) in octave relation to each other in the lower manual keyboard 128.

According to the principle of the invention, four signals generated by a series of signal sources such as an oscillator 151 and frequency dividers 152, 153 and 154 are distributed, through a mixing network having a series connection of eight impedance elements, i.e. resistors 137, 138, 139, 140, 141, 142, 143 and 150, to five keyswitches 129, 130, 131, 132 and 136 in octave relation to each other so as to form a series of five composite tone signals of the invention. Keyswitches 132, 131, 130 and 129 of the upper manual keyboard 127 are provided with higher four composite tone signals, higher in pitch, of a series of five composite tone signals constructed of said four signals of signal sources. On the other hand, similarly according to the principle of the invention, said four signals of signal sources are distributed, through another mixing network having a series connection of eight impedance elements, i.e. resistors .137, 144, 145, 146, 147, 148, 149 and 150, to five keyswitches 129, 133, 134, 135 and 136 in octave relation to each other so as to form another series of five composite tone signals of the invention. Keyswitches 136, 135, 134 and 133 of the lower manual keyboard 128 are provided with lower four composite tone signals, lower in pitch of another series of five composite tone signals constructed of said four signals of signal sources. 7

In this case, keyswitches and 133 are supplied with composite tone signals constructed of a fundamental signal from oscillator 151 and a sub-octave signal from frequency divider 152, but said composite tone signals may not necessarily have the same mixing ratio of a suboctave signal to a fundamental signal on the premise that said composite tone signals are heard as if they are of the same pitch. Similarly, each pair of composite tone signals switched on by keyswitches 131 and 134, or keyswitches 132 and 135, may not necessarily have the same mixing ratio.

On the other hand, people perceive one octave interval sensation between composite tone signals derived from keyswitches 129 and 130, between composite tone signals derived from keyswitches 130 and 131, between composite tone signals derived from keyswitches 131 and 132, or between composite tone signals derived from keyswitches 132 and 136, respectively, or, between composite tone signals derived from keyswitches 129 and 133, between composite tone signal derived from keyswitches 133 and 134, between composite tone signals derived from keyswitches 134 and 135 or between composite tone signals derived from keyswitches 135 and 136, respectively. Therefore, the keys of the keyboards has a four octaves musical interval, but there is a three octaves interval in the frequency of the signals of the signal sources.

By employing the present system for distributing signals, signal sources in a less octave range than that of keyswitches produce composite tone signals corresponding to keys of the whole keyboards. Consequently, the cost of an electronic musical instrument having the signal distributing system according to the invention can be lower than conventional electronic musical instruments.

Such a signal distributing system is, of course, applicable for electronic musical instruments having three or more manual keyboards.

It is possible that difference signals derived from difference signal generators, such as perfect fourth type difference signal generators and perfect fifth type difference signal generators, which will be defined below are substituted for signals generated by signal sources such as oscillators and frequency dividers.

The perfect fourth type difference signal generator is defined as a kind of tone generator which has a nonlinear circuit and a low pass filter, and which mixes two signals in a pitch interval of perfect fourth. That is, two signals in a frequency ratio of about -4fz3f can be combined into a perfect fourth type difference signal having a difference frequency about f(=4f3f) by said perfect fourth type difference signal generator. In other words, a higher signal of said two signals is higher in pitch by two octaves than the resultant perfect fourth type difference signal and another of said two signals is lower in pitch by perfect fourth pitch interval than said higher signal.

The perfect fifth type difference signal generator is defined as a kind of tone generator which has a nonlinear circuit and a low pass filter, and which mixes two signals in a pitch interval of perfect fifth. That is, two signals in a frequency ratio of about 2]:3f can be combined into a perfect fifth type difference signal having a difference frequency about f(=3f-2f) by said perfect fifth type difference signal generator. In other words, a lower signal of said two signals is higher in pitch by 17 one octave than the resultant perfect fifth type difference signal and another of said two signals is higher in pitch by perfect fifth pitch interval than said lower signal.

Referring to FIG. 8 showing an embodiment which is prepared by replacing two frequency dividers with two difference signal generators in low frequency range, C series of composite tone signals C C C C C and C corresponding to keyswitches 499, 298, 497, 496, 495 and 494, respectively, are produced in accordance with the invention.

A signal generated by an oscilla or 451 is a sine-wavelike signal having a fundamental frequency 167 HZ. and is fed to a waveform changing means 449 such as a clipper circuit in order to convert said sine-wave-like signal into a rectangular wave signal in the same frequency 16f Hz. as said sine-wave-like signal and in the inverse phase of said sine-wave-like signal. A sine-wave-like signal hereinbefore and hereinafter is defined, for convenience, as a signal having such a waveform, for example, as a sine wave or a distorted sine wave. The signal having a frequency 16 derived from said waveform changing means 449 is successively divided by a factor of two by means of the successive frequency dividers 452 and 453 in order to produce signals having frequencies 8 and 47, respectively.

A signal generated by an oscillator 454 is a sine-wavelike signal having a fundamental frequency 12 Hz. and is fed to a waveform changing means 450 such as clipper circuit in order to convert said sine-wave-like signal into a rectangular Wave signal having the same frequency 12 as said sine-wave-like signal. The signal in a frequency 12 is derived from said waveform changing means 450 and is sucessively divided by a factor of two by means of the successive frequency dividers 455 and 456 in order to produce signals having frequencies 6 and 3f, respectively.

' Since the oscillators 451 and 454 are tuned in C tone and G tone, respectively, in accordance with equal temperament scale, the clipper circuit 449 and dividers 452 and 453 act as C series of signal sources having frequencies, 16 8 and 4 respectively, while the clipper circuit 450 and dividers 455 and 456 act as G series of signal sources having frequency 12 6f and 3f, respectively. Frequencies 12f, 6f and 3 of G series of signal sources are slightly lower than frequencies 12 6 and 31, respectively, because of the equal temperament.

The pitch interval between the frequencies 16 and 12 is a perfect fourth musical interval. And the frequency 12f is lower by a perfect fourth musical interval than the frequency 167.

The pitch interval between the frequencies 6f and 4f is a perfect fifth musical interval, and the frequency 6f is higher by a perfect fifth musical interval than the frequency 4f.

The frequency interval between the frequencies 47 and 37' is a perfect fourth musical interval, and the frequency 3f is lower by a perfect fourth musical interval than the frequency 4 A signal in a frequency 4 generated by the divider 453 and a signal in a frequency 6f generated by the divider 455 are mixed together through resistor 471 and 472 respectively at an input terminal 442 of a perfect fifth type difference signal generator 446, in which the input terminal 442 is shunted to the earth through a parallel circuit of a shunt resistor 488, a diode 489 acting as a non-linear circuit and a capacitor 490 acting as a low pass filter and is connected to an output terminal '444. Said perfect fifth type difference signal generator 446 produce a perfect fifth type difference signal having a frequency 2f (=6f4f) by the diode 489 and the capacitor 490. Said frequency 2 is slightly lower, because of the equal temperament, than the frequency 2f corresponding to a half of the frequency 4 Said perfect fifth type difference signal generator 446 acts as one of C series of signal sources and has a similar function to the clipper circuit 449 or the frequency dividers 452 and 453.

A signal in a frequency 4 generated by the divider 453 and a signal in a frequency 3 generated by the divider 456 are mixed together through resistors 478 and 479 respectively at an input terminal 443 of a perfect fourth type difference signal generator 447, in which the input terminal 443 is shunted to the earth through a parallel circuit of a shunt resistor 491, a diode 492 acting as a non-linear circuit and a capacitor 493 acting as a low pass filter and is connected to an output terminal 445. Said perfect fourth type difference signal generator 447 produces a perfect fourth type difference signal having a frequency f(:4f3f) by the diode 492 and the capacitor 493. Said frequency f is slightly higher, because of the equal temperament, than the frequency 7 corresponding to a quarter of the frequency 4 Said perfect fourth type difference signal generator 447 acts as another one of C series of signal sources and has a similar function to a clipper circuit 450, the frequency dividers 455 and 456 or the perfect fifth type difference signal generator 446 mentioned previously. Thus, five signal sources having frequencies 16f, 8f, 4 2f and f are prepared. Five signals of said five signal sources are distributed to six keyswitches 494, 495, 496, 497, 498 and 499 through a mixing network having a series connection of eight resistors 457, 458, 459, 461, 462, 465, 466 and 470 and another resistor 477 so as to form six composite tone signals C C C C C and C respectively according to the invention.

A perfect fourth type difference signal in a frequency f is generated by the perfect fourth type difference signal generator 447 and is fed to keyswitch 499 through a resistor 477 in order to produce a composite tone signal C1.

A perfect fifth type difference signal in a frequency 2 is generated by the perfect fifth type difference signal generator 446 and is fed to a keyswitch 498 through resistor 470 in order to produce the composite tone signal C A perfect fifth type difference signal in a frequency 2 generated by said perfect fifth type difference signal generator 446 and a signal in a frequency 4 generated by the frequency divider 453 are mixed together, in a mixing ratio similar to that shown in FIG. 1 or FIG. 3 and are fed to a keyswitch 497, through a resistor 466 and 465 respectively so as to form a composite tone signal C There is one octave interval sensation between said composite tone signal C and said composite tone signal C A signal in a frequency 4f generated by the frequency divider 453 and a signal in a frequency 8 generated by the frequency divider 452 are mixed together in a mixing ratio similar to that shown in FIG. 1 or FIG. 3, and are fed to keyswitch 496 through resistors 462 and 461 so as to form a composite tone signal C And there is one octave interval sensation between said composite tone signal C and said composite tone signal C A signal in a frequency 8) generated by the frequency divider 452 and a signal in a frequency 16f generated by the clipper circuit 449 are mixed together in a mixing ratio similar to that shown in FIG. 1 or FIG. 3, and are fed to keyswitch 495 through resistors 459 and 458 so as to form a composite tone signal C And there is one octave interval sensation between said composite tone signal C and said composite tone signal C A signal in a frequency 16 generated by the clipper circuit 449 is fed to keyswitch 494 through a resistor 457 so as to form a composite tone signal C which is a rectangular wave signal. And there is one octave interval sensation between said composite tone signal C and said composite tone signal C Thus, these six composite tone signals C C C C C and C are produced in a manner similar to that of FIG. 1 or FIG. 3 by five signals of five tone generators, i.e. the clipper circuit 449,

the frequency divider 452, the frequency divider 453, the perfect fifth type difference signal generator 446 and the perfect fourth type difference signal generator 447. Consequently, said six composite tone signals 0,, C C C C and C are produced by five signal sources comprising the clipper circuit 449 and two frequency dividers 452 and 453, and two difference signal generators 446 and 447.

However, said six composite tone signals C C C C C and C have very different tone color from each other. For example, the signals produced by said perfect fifth type and perfect fourth type difference signal generators 446 and 447 are provided with a very weak upper harmonics by means of low pass filters but the signals produced by said clipper circuit and frequency dividers have rich upper harmonics.

In order to modify overtone spectra of said composite tone signals C C C C C and C additional signals from signals sources are mixed with each of composite tone signals. Detail modification will be explained hereinafter.

A keyswitch 499 is supplied additionally with four signals generated by the clipper circuit 449, the frequency divider 452, the frequency divider 453 and the perfect fifth type difference signal generator 446 through additional resistors 473, 474, 475 and 476, respectively, in order to enrich upper harmonics of the composite tone signal C Three signals generated by the clipper circuit 449, the frequency divider 452 and the frequency divider 453 are additionally fed to the keyswitch 498 through the additional resistors 467, 468 and 469, respectively, in order to enrich upper harmonics of the composite tone signal Two signals generated by the clipper circuit 449 and the frequency divider 452 are additionally fed to the keyswitch 497 through additional resistors 463 and 464, respectively, in order to enrich upper harmonics of the composite tone signal C 1 One signal generated by the clipper circuit 449 is additionally fed to the keyswitch 496 through an additional resistor 460 in order to enrich upper harmonics of the composite tone signal C With respect to the composite tone signal C no additional signal is fed to the keyswitch 495, because there is no signal sources having a higher frequency than frequency 16f generated by clipper circuit 449.

A sine-wave-like signal generated by the oscillator 451 is additionally fed to the keyswitch 494 through additional resistor 448 in order to partially cancel the amplitude of the fundamental frequency of said composite tone signal C and to emphasize the upper harmonics of said composite tone signal C relatively. In other words, said sine-wave-like signal is mixed with said composite tone signal, i.e. a rectangular wave signal. In order to furthermore emphasize the upper harmonics of the composite tone signal C 2. high pass filter, a capacitor or other circuits may be substituted for the resistor 448 or 457.

Therefore, these enriched six composite tone signals 0,, C C C C and C are much a like in tone color because they have octavely related signals additionally and have abundant upper harmonics.

. The same manner as described hereinbefore in accordance with six composite tone signals of C series is also applicable for producing composite tone signals of each of the other eleven series, namely Cit series, D series, Dil series, E series, F series, Fit series, G series, Git series, A series, Ail series and Bit series.

Five composite tone signals of each of six series, namely Cll series, D series, Dit series, E series, P series and Fit series, are produced by using four signal sources, i.e. a clipper circuit, a frequency divider, a perfect fifth type difference signal generator and a perfect fourth type difference signal generator.

Five composite tone signals of each of five series, namely G series, Git series, A series, At? series and B series, are produced by using four signal sources, i.e. a clipper circuit, two frequency dividers and a perfect fifth type difference signal generator.

Consequently, sixty-one composite tone signals are produced by forty-nine signal sources. In other words, sixtyone composite tone signals are produced by twelve clipper circuits and eighteen frequency dividers.

Referring to FIG. 9 showing another illustration of an arrangement hereinbefore described with FIG. 8 for producing sixty-one composite tone signals, namely composite tone signals C Cfli, D F li, G C F il',G ...,C ...,C ,C 1$...,C ...,andC in an order of pitch from the lowest pitch tone signal, these sixty-one composite tone signals C to C are produced by only twelve clipper circuits and eighteen frequency dividers. Eighteen frequency dividers produce signals from G to C, as indicated by a shaded portion Y of FIG. 9 and twelve clipper circuits produce signals from C t to C as indicated by another shaded portion X of FYG. 9Teven signals from C to F it are generated by perfect fourth type differenc? signal generators. Twelve signals from G, to F lt are generated by perfect fifth type difference signal genefators.

Forty nine signals, i.e. seven perfect fourth type difference signals from C to F t, twelve perfect fifth type difference signals from G, fi i, and thirty signals from G to C are distributed to sifiy -one keys corresponding tFcomEsite tone signals C to C through a signal distributing system of the present invention.

Consequently, sixty-one composite tone signals C to C are produced from twelve clippers and eighteen frequency dividers.

The concept of the novel composite tone signals according to the invention can be, applied not only to the whole range of the keyboard of an electronic musical instrument, but also to a part of the keyboard in such a way that the signal mixing networks mix some of signals generated by the signal generator system so as to produce composite tone signals for only a part of the keyboard.

In addition, the concept of the novel composite tone signals according to the invention can be applied to an electronic musical instrument having two or more keyboards in such a way that some of said keyboards control said novel composite tone signals and the other of said keyboards control conventional tone signals.

While particular embodiments of the invention have been shown and described, it will be apparent to those skilled in the art that numerous modifications and variations can be made in the form and construction thereof Without departing from the fundamental principles of the invention. It is, therefore, desired, by the following claims, to include within the scope of the present invention all similar and modified forms of the apparatus disclosed and by which the results of the invention can be obtained.

What is claimed is:

1. An electronic musical instrument comprising in combination:

(1) a generator system having at least twelve series of signal sources for generating signals of pitches corresponding to the musical scale, each of said at least twelve series of signal sources being in an arrangement of octave relation to each other,

(2) a keyswitch system having at least twelve series of keyswitches which are capable of switching on tone signals corresponding to depressed keys, each of said at least twelve series of keyswitches being in an arrangement of octave relation to each other,

(3) an output system which is coupled to said keyswitch system and which includes an amplifier and an electro-acoustic translating means, and

(4) a signal distributing system which is coupled between said generator system and said keyswitch system and which includes at least twelve mixing networks,

(a) each of said at least twelve mixing networks having an even number of impedance elements connected in series and being coupled between each of said at least twelve series of signal sources and each of said at least twelve series of keyswitches in such a way that a bottom terminal, junction points in an even order from said bottom terminal and a top terminal of said even number of impedance elements are connected to keyswitches of each of said at least twelve series of keyswitches, respectively, and further in such a way that junction points in an odd order from said bottom terminal are connected to signal sources at each of at least twelve series of signal sources, respectively,

(b) and each of said at least twelve mixing networks producing a series of composite tone signals corresponding to said keyswitches of each of said at least twelve series of keyswitches so that said series of composite tone signals have sub-octave signals, of which the amplitude percent level shows a progressive increasement from zero percent level to 100 percent level as said composite tone signals ascend in octave with octave ascents of said keyswitches, said increasement being characterized in that said increasement proceeds stepwise and has the first step not more in the increasement than percent and each successive step not less in the increasement than the previous step.

2. The electronic musical instrument as defined in claim 1, wherein said at least twelve series of signal sources comprise oscillators and frequency dividers.

3. The electronic musical instrument as defined 1n claim 1, wherein said at least twelve series of signal sources comprise oscillators, frequency dividers and difference signal generators. 4. The electronic musical instrument as defined in claim 1, wherein said difference signal generators comprise perfect fifth type difference signal generators, each of which produces a perfect fifth type difference signal by mixing two signals in pitch intenval of perfect fifth to each other, the lower signal of said two signals being higher in pitch by one octave than said perfect fifth type dif ference signal, the other of said two signals being higher in pitch by perfect fifth pitch interval than said lower signal of said two signals. 5. The electronic musical instrument as defined in claim 3, wherein said difference signal generators comprise perfect fourth type difference signal generators, each of which produces a perfect fourth type difference signal by mixing two signals in pitch interval of perfect fourth to each other, the higher signal of said two signals being higher in pitch by two octaves than said perfect fourth type difference signal, the other of said two signals being lower in pitch by perfect fourth pitch interval than said higher signal of said two signals.

6. The electronic musical instrument as defined in claim 3, wherein said difference signal generators comprise perfect fifth type difference signal generators and perfect fourth type difference signal generators,

each of said perfect fifth type difference signal generators being able to produce a perfect fifth type difference signal by mixing two signals in pitch interval of perfect fifth to each other, the lower signal of said two signals being higher in pitch by one octave than said perfect fifth type difference signal and the other of said two signals being higher in pitch by perfect fifth pitch interval than said lower signal of said two signals, and

each of said perfect fourth type difference signal generators being able to produce a perfect fourth type difference signal by mixing another two signals in pitch interval of perfect fourth to each other, the higher signal of said another two signals being higher in pitch by two octaves than said perfect fourth type difference signal and the other signal of said another two signals being lower in pitch by perfect fourth pitch interval than said higher signal of said another two signals.

7. The electronic musical instrument as defined in claim 6, wherein said difference signal generators comprise seven said perfect fourth type difference signal generators as the lowest seven signal sources and twelve said perfect fifth type difference signal generators as the lowest twelve signal sources next to said lowest seven signal sources.

8. The electronic musical instrument as defined in claim 2, wherein each of said oscillators comprises a pair connection of an oscillator generating a sine-wave-like signal and a waveform changing means which converts said sinewave-like signal into a rectangular wave signal having the same frequency as said oscillator and having the inverse phase of said sine-wave-like signal,

said sine-wave-like signal being mixed with said rectangular wave signal.

9. The electronic musical instrument as defined in claim 3, wherein each of said oscillators comprises a pair connection of an oscillator generating a sine-wave-like signal and a waveform changing means which converts said sinewave-like signal into a rectangular wave-signal having the same frequency as said oscillator and having the inverse phase of said sine-wave-like signal,

said sine-wave-like signal being mixed with said rectangular wave signal.

10. The electronic musical instrument as defined in claim 1, wherein said even number of impedance elements including at least one high pass filter circuit.

11. The electronic musical instrument as defined in claim 1, wherein one or more said composite tone signals of said series of composite tone signals are mixed with at least one of additional signals of said signal sources of each of said at least twelve series of signal sources, said at least one of additional signals acting as upper harmonics of said one or more composite tone signals.

12. An electronic musical instrument comprising in combination:

(1) a generator system having at least twelve series. of

signal sources for generating signals of pitches corresponding to the musical scale, each of said at least twelve series of signal sources being in an arrangement of octave relation to each other,

(2) a keyswitch system having at least twelve series of keyswitches which are capable of switching on tone signals corresponding to depressed keys, each of said at least twelve series of keyswitches being in an arrangement of octave relation to each other,

(3) an output system which is coupled to said keyswitch system and which includes an amplifier and an electro-acoustic translating means, and

(4) a signal distributing system which is coupled between said generator system and said keyswitch system and which includes at least twelve mixing networks,

(a) each of said at least twelve mixing networks having an even number of impedance elements connected in series and being coupled between each of said at least twelve series of signal sources and each of said at least twelve series of keyswitches in such a way that a bottom terminal, junction points in an even order from said bottom terminal and a top terminal of said impedance elements are connected to keyswitches of each of at least twelve series of keyswitches, respectively, and further in such a way that junction points in an odd order from said bottom terminal are connected to signal sources of each of at least twelve series of signal sources, and

having further impedance elements through which double-suboctave signals are fed to keyswitches of each of said at least twelve series of keyswitches, and which are connected in such a way that a junction point in an odd order is connected through a further impedance element to a junction point in the even order after the next even order and the last junction point in an odd order is connected through an additional imped- 35 ance element to an additional keyswitch,

and

(b) each of said at least twelve mixing networks producing a series of composite tone signals corresponding to said keyswitches of each of said at least twelve series of keyswitches so that said series of composite tone signals have double-suboctave signals, of which the amplitude percent level shows a progressive increasement from zero percent level to percent level as said composite tone signals ascend in octave with octave ascents of said keyswitches, said increasement being characterized in that said increasement proceeds stepwise and has the first step not more in the increasement than 20 percent and each successive step not less in the increasement than the previous step, and

have suboctave signals, of which the amplitude percent level shows another progressive increasement from zero percent level as said composite tone signals ascend in octave with octave ascents of said keyswitches, said another progressive increasement proceeds stepwise and has the first step not more in the increasement than 20 percent.

References Cited UNITED STATES PATENTS 6/ 1951 Larsen 84-1.19 6/1936 Yungblut 84--l.17 1/1939 Williams 84-1.23 X 6/1951 Mor-k 841.17 10/1951 Knoblaugh et a1. 841,21 X 2/1961 Anderson 84-1.22 11/ 1966 Cookerly et a1 841.01

WARREN E. RAY, Primary Examiner US. Cl. X.R. 

